Implements view tags as proposed by @UkoeHB in MRL issue
https://github.com/monero-project/research-lab/issues/73
At tx construction, the sender adds a 1-byte view tag to each
output. The view tag is derived from the sender-receiver
shared secret. When scanning for outputs, the receiver can
check the view tag for a match, in order to reduce scanning
time. When the view tag does not match, the wallet avoids the
more expensive EC operations when deriving the output public
key using the shared secret.
There are quite a few variables in the code that are no longer
(or perhaps never were) in use. These were discovered by enabling
compiler warnings for unused variables and cleaning them up.
In most cases where the unused variables were the result
of a function call the call was left but the variable
assignment removed, unless it was obvious that it was
a simple getter with no side effects.
These are functions that check whether a tx is in the db, so whether
it is there or not is really not interesting, and it seems to scare
people from time to time
On startup, it checks against the difficulty checkpoints, and if any mismatch is found, recalculates all the blocks with wrong difficulties. Additionally, once a week it recalculates difficulties of blocks after the last difficulty checkpoint.
If a db resize happened, the txpool meta cursor might be stale,
and was not being renewed when necessary.
It would cause this SEGSEGV:
in mdb_cursor_set ()
in mdb_cursor_get ()
in cryptonote::BlockchainLMDB::get_txpool_tx_blob(crypto::hash const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, cryptonote::relay_category) const ()
in cryptonote::tx_memory_pool::get_transaction(crypto::hash const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, cryptonote::relay_category) const ()
in cryptonote::t_cryptonote_protocol_handler<cryptonote::core>::handle_notify_new_fluffy_block(int, epee::misc_utils::struct_init<cryptonote::NOTIFY_NEW_FLUFFY_BLOCK::request_t>&, cryptonote::cryptonote_connection_context&) ()
If the peer (whether pruned or not itself) supports sending pruned blocks
to syncing nodes, the pruned version will be sent along with the hash
of the pruned data and the block weight. The original tx hashes can be
reconstructed from the pruned txes and theur prunable data hash. Those
hashes and the block weights are hashes and checked against the set of
precompiled hashes, ensuring the data we received is the original data.
It is currently not possible to use this system when not using the set
of precompiled hashes, since block weights can not otherwise be checked
for validity.
This is off by default for now, and is enabled by --sync-pruned-blocks
The db txn in add_block ending caused the entire overarching
batch txn to stop.
Also add a new guard class so a db txn can be stopped in the
face of exceptions.
Also use a read only db txn in init when the db itself is
read only, and do not save the max tx size in that case.
